Total hip replacement (THR) is a surgical procedure in which various components of a patient's hip joint are replaced with artificial components in order to restore functionality of the patient's hip.
In one common THR procedure, an artificial acetabular cup is implanted in place of the patient's natural acetabulum, and a femoral prosthesis is implanted into the patient's femur. The femoral prosthesis has a head that engages the artificial acetabular cup to allow the femoral prosthesis/acetabular cup combination to function much like the natural hip joint. However, the ability of an artificial hip joint to function like the patient's natural hip joint depends on how well the components of the artificial hip fit when implanted into a particular patient.